Conventionally, an image processing apparatus for processing an image captured by an image sensing apparatus such as a digital camera records the image data representing the captured image in a recording unit following compression or as is if compression has not been applied. Further, the image processing apparatus reads the image data out of the recording unit at the time of playback and displays the image on the display screen of a monitor, irrespective of the attitude of the camera at the time of image sensing, following expansion if the data has been compressed or as is if the data has not been compressed.
FIGS. 10A to 10C illustrate the relationship between the attitude of a camera when an image is taken and the image displayed on the monitor. FIG. 10A shows the observed image that appears in an image sensing area viewed from the finder of the camera at the time of image sensing. This illustrates a situation where an image is taken with a camera attitude in which the image sensing area is long in the width direction (this is referred to as “landscape orientation”). FIG. 10B illustrates conceptually the image data that is output from an image sensing device when an image is taken in the landscape orientation shown in FIG. 10A. FIG. 10C illustrates this image when it has been displayed on a display unit such as a TV. In this case it is understood that the direction of the image displayed is the same as the direction of the observed image as viewed from the finder at the time of image sensing.
FIGS. 11A to 11C similarly illustrate the relationship between the attitude of the camera when an image is taken and the image displayed on the monitor. FIG. 11A shows the observed image that appears in the image sensing area viewed from the finder of the camera at the time of image sensing. This illustrates a situation where an image is taken with a camera attitude in which the image sensing area is long in the height direction (referred to as “portrait orientation”). In this example, the camera has been rotated 90° in the clockwise direction. FIG. 11B illustrates conceptually the image data that is output from the image sensing device when an image is taken in the portrait orientation shown in FIG. 11A. FIG. 11C illustrates this image when it has been displayed on a display unit such as a TV. In this case the image displayed on the display unit has been rotated by 90° in the counter-clockwise direction with respect to the vertical direction of the observed image viewed from the finder by the user at the time of image sensing.
If FIGS. 10C and 11C are compared, it will be appreciated that the direction of the displayed image is correct in FIG. 10C for the case where the image was taken in the landscape orientation. As a result, one can enjoy the image as is without experiencing an odd sensation. However, in FIG. 11C where the image was taken in the portrait orientation, the direction, in which the image has been rotated 90° in the counter-clockwise direction, of the displayed image is wrong. This image cannot be enjoyed as is without experiencing an odd sensation.
In order to deal with this problem, the specification of Japanese Patent Application Laid-Open No. 10-233993 proposes detecting the attitude of the camera at the time of image sensing using a camera attitude sensor and, in accordance with the detected camera attitude, changing the order in which image data, which has been stored in a frame memory, is read out, thereby generating compressed image data representing an image in which the direction of the observed image at the time of image sensing becomes the same as the direction of the image displayed on a display unit.
Further, the specification of Japanese Patent Application Laid-Open No. 10-336660 proposes providing a camera orientation detector for detecting whether the longitudinal direction in an image sensing area of the camera is the portrait orientation or the landscape orientation, and two types of quantization tables, namely one for the portrait orientation and one for the landscape orientation. A quantization table selector selects one of the quantization tables in accordance with the camera orientation and outputs the selected table to a quantization processing circuit. Further, DCT (Direct Cosine Transform) coefficients that have been output from a DCT processing circuit are quantized in the quantization processing circuit using the quantization table selected.
However, in a case where processing for rotation by 90° in the clockwise direction or 270° in the clockwise direction (namely by 90° in the counter-clockwise direction) at the time of display is executed in accordance with attitude information, which prevailed at the time of image sensing, that has been appended to the image data, so that an image captured in the portrait orientation can be enjoyed without an odd sensation, the rotation processing takes a considerable time. Since the time required by this rotation processing lengthens as the image information, namely the number of pixels, increases, there is an increase in waiting time from the moment a switch member for reproducing and displaying an image is operated to the moment the image is displayed.